Question 1

Which of the following statements best describes the initiation step in the free-radical chlorination of methane?

Accepted Answer

It involves the homolytic cleavage of a chlorine molecule to generate two chlorine atoms (free radicals) using heat or light.

Question 2

What is the overall balanced chemical equation for the chlorination of methane?

Accepted Answer

$$ \mathrm{CH_4$ + Cl_2$ \rightarrow CH_3Cl + HCl} $$

Question 3

Which step in the free-radical chain reaction mechanism is responsible for the formation of the organic product in methane chlorination?

Accepted Answer

Propagation step where the methyl radical reacts with a chlorine molecule to form chloromethane and a chlorine atom.

Question 4

Which of the following best explains why the chlorination of methane is considered a chain reaction?

Accepted Answer

One photon of light initiates the reaction, but many molecules of product are formed because the reactive intermediates regenerate and continue the process.

Question 5

Which of the following is a termination step in the free-radical chlorination of methane?

Accepted Answer

Combination of a methyl radical and a chlorine atom to form chloromethane.

Question 6

What is the effect of increasing temperature on the rate of a chemical reaction according to the Arrhenius equation?

Accepted Answer

Increasing temperature increases the rate constant $$k$$ because more molecules have the required activation energy.

Question 7

Given the equilibrium constant $$K_{eq}$$ for the chlorination of methane is $$1.1 	imes 10$$^{19}$$, what does this indicate about the reaction?

Accepted Answer

The reaction goes nearly to completion, favoring the formation of products.

Question 8

Which of the following best describes the difference between homolytic and heterolytic bond cleavage?

Accepted Answer

Homolytic cleavage produces two radicals, each atom takes one electron; heterolytic cleavage produces ions, with both electrons going to the more electronegative atom.

Question 9

Which of the following factors contributes to the stability of a carbocation?

Accepted Answer

Hyperconjugation and inductive effects from alkyl substituents.

Question 10

Which of the following statements about free radicals is correct?

Accepted Answer

Free radicals are stabilized by alkyl substituents; tertiary radicals are more stable than secondary, which are more stable than primary.

Question 11

Which of the following is true regarding the entropy change ($$\Delta S^\circ) in a $$chemical reaction?

Accepted Answer

Increasing the number of particles, heat, or volume increases entropy.

Question 12

Which of the following is the correct expression for the free energy change ($$\Delta G^\circ) in $$terms of enthalpy and entropy?

Accepted Answer

$$ \Delta G^\circ = \Delta H^\circ - T \Delta S^\circ $$

Question 13

Which of the following statements about the Hammond Postulate is correct?

Accepted Answer

The structure of the transition state resembles the structure of the closest stable species in energy.

Question 14

Which of the following is a real-world application of radical inhibitors?

Accepted Answer

They are added to food to retard spoilage by radical chain reactions.

Question 15

Which of the following best describes the basicity of carbanions compared to amines?

Accepted Answer

Carbanions are more basic and stronger nucleophiles than amines because of the negative charge on carbon.

Question 16

Which of the following statements about carbenes is correct?

Accepted Answer

Carbenes have both a lone pair of electrons and an empty p orbital, allowing them to act as both nucleophiles and electrophiles.

Question 17

In the chlorination of isobutane, primary hydrogens react with Cl$$_2$$ about 1.0 times as fast as tertiary hydrogens, which react 5.5 times as fast. If isobutane has 9 primary hydrogens and 1 tertiary hydrogen, what is the expected product ratio of tertiary to primary chlorinated products?

Accepted Answer

The ratio is $$5.5:9.0$$, so the fraction of tertiary product is $$\frac{5.5}{5.5+9.0} \approx 0.38.$$

Question 18

Which of the following is true about the activation energy ($$E_a) $$and reaction rate?

Accepted Answer

A higher activation energy results in a slower reaction rate.

Question 19

Which of the following correctly ranks the stability of carbon intermediates from most to least stable?

Accepted Answer

Carbocation: $$3^\circ \u003e 2^\circ \u003e 1^\circ \u003e 	ext{methyl}$$; Carbanion: $$	ext{methyl} \u003e 1^\circ \u003e 2^\circ \u003e 3^\circ$$; Radical: $$3^\circ \u003e 2^\circ \u003e 1^\circ \u003e 	ext{methyl}$$

Chapter 4: The Study of Chemical Reactions (Organic Chemistry)

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